Cooling simulation method, cooling simulation program, cooling simulation device, and method of cooling workpiece

ABSTRACT

A cooling simulation method is a cooling simulation method for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with the workpiece. In the cooling simulation method, a flow velocity of the coolant on the surface of the workpiece is calculated by a flow analysis of the coolant by a thermal fluid simulation, and the temperature change inside the workpiece is calculated based on a temperature of the surface of the workpiece and the calculated flow velocity.

BACKGROUND Technical Field

An embodiment of the present invention relates to a cooling simulation method, a cooling simulation program, a cooling simulation device, and a method of cooling a workpiece.

Related Art

In a quenching treatment of a steel component, a workpiece is heated to a temperature equal to or higher than an austenite transformation point, and then a coolant is brought into contact with a workpiece surface to rapidly cool the workpiece. This cooling behavior affects characteristics such as a hardness, a deformation amount, and a residual stress of each portion of the workpiece after quenching. Since there are many factors such as a material and a shape of the workpiece, a cooling method, a workpiece installation situation during cooling, and a type and a flow rate of the coolant as factors affecting the cooling behavior, it takes a lot of time and cost to determine optimum cooling conditions for the quenching treatment by trial and error in an actual machine. For this reason, in recent years, it has been attempted to predict the cooling behavior by a thermal fluid simulation by a numerical analysis method such as a finite volume method, a difference method, or a particle method.

However, in order to simulate cooling with practically sufficient accuracy, it is necessary to consider the boiling phenomenon of the coolant. Since the boiling phenomenon is a complicated phenomenon in which film boiling, nucleate boiling, and the like exist, in order to strictly simulate the cooling behavior of the workpiece, including the boiling phenomenon of the coolant, an amount of calculation becomes enormous and a large amount of calculation time is required.

Patent literature 1: JP-A-2010-230331

SUMMARY

An object of an embodiment of the present invention is to provide a cooling simulation method, a cooling simulation program, a cooling simulation device, and a method of cooling a workpiece that can shorten a calculation time.

A cooling simulation method according to an embodiment of the present invention is a cooling simulation method for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece. In the cooling simulation method, a flow velocity of the coolant on the surface of the workpiece is calculated by a flow analysis of the coolant by a thermal fluid simulation, and the temperature change inside the workpiece is calculated based on a temperature of the surface of the workpiece and the calculated flow velocity.

A cooling simulation program according to an embodiment of the present invention is a cooling simulation program for predicting a temperature change inside a workpiece when a coolant is brought into contact with a surface of the workpiece. The cooling simulation program causes a computer to calculate a flow velocity of the coolant on the surface of the workpiece by a thermal fluid simulation, and calculate the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow rate.

A cooling simulation device according to an embodiment of the present invention is a cooling simulation device that predicts a temperature change inside a workpiece when a coolant is brought into contact with a surface of the workpiece. The cooling simulation device includes a calculator that calculates a flow velocity of the coolant on the surface of the workpiece by a thermal fluid simulation, and calculates the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.

A method of cooling a workpiece according to an embodiment of the present invention includes determining a cooling condition by the cooling simulation method, and cooling the workpiece under the determined condition.

According to an embodiment of the present invention, it is possible to realize a cooling simulation method, a cooling simulation program, a cooling simulation device, and a method of cooling a workpiece that can shorten a calculation time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram illustrating a cooling simulation device according to a first embodiment, and FIG. 1B is a block diagram illustrating a calculator;

FIGS. 2A and 2B are diagrams illustrating an operation of the cooling simulation device according to the first embodiment, in which FIG. 2A illustrates a simulation of a heating step, and FIG. 2B illustrates a simulation of a cooling step;

FIG. 3 is a graph illustrating a relation between a workpiece surface temperature, a flow velocity of a coolant, and a heat transfer coefficient on a workpiece surface, in which a horizontal axis represents the workpiece surface temperature and a vertical axis represents the heat transfer coefficient on a workpiece surface;

FIG. 4 is a flowchart illustrating a heating simulation method in the first embodiment;

FIG. 5 is a plan view illustrating a cooling device assumed in the first embodiment;

FIG. 6 is an end view illustrating the cooling device assumed in the first embodiment;

FIG. 7 is a flowchart illustrating a cooling simulation method according to the first embodiment;

FIG. 8 is a flowchart illustrating a cooling simulation method according to a second embodiment;

FIG. 9 is a flowchart illustrating a method of cooling a workpiece according to a third embodiment;

FIG. 10A is a perspective transparent view illustrating a cooling device manufactured and assumed in a test example, and FIG. 10B is a diagram illustrating an initial value of a workpiece surface temperature;

FIG. 11A is a diagram illustrating an appearance of a coolant calculated in a test example, and FIG. 11B is a diagram illustrating a flow velocity distribution; and

FIGS. 12A and 12B are graphs illustrating a workpiece surface temperature change with a horizontal axis representing a time and a vertical axis representing a temperature, in which FIG. 12A illustrates an actual measured value, and FIG. 12B illustrates a calculated value.

DETAILED DESCRIPTION First Embodiment

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1A is a block diagram illustrating a cooling simulation device according to the present embodiment, and FIG. 1B is a block diagram illustrating a calculator.

FIGS. 2A and 2B are diagrams illustrating an operation of the cooling simulation device according to the present embodiment, in which FIG. 2A illustrates a simulation of a heating step, and FIG. 2B illustrates a simulation of a cooling step.

A cooling simulation device 1 (hereinafter, also simply referred to as the “device 1”) according to the present embodiment is a device that predicts a temperature change inside a workpiece when a coolant is brought into contact with the workpiece, and is, for example, a device that simulates a cooling step of a quenching treatment. In the present specification, the “workpiece” is a steel product to be a quenching treatment target.

As illustrated in FIG. 1A, the device 1 includes an inputter/outputter 10, a calculator 20, and a storage 30. A general-purpose computer or a dedicated computer may be used in the device 1.

The inputter/outputter 10 is provided with, for example, a signal terminal or a communication device, and receives data from the outside and outputs data to the outside. The data input to the inputter/outputter 10 is data to be described later, and includes various conditions of a cooling simulation in particular. The data includes, for example, a shape of the workpiece, an initial value of the temperature of the workpiece, a shape of a cooling jacket, a physical property of the coolant, and a flow rate of the coolant. The shape of the cooling jacket also includes the size, number, and arrangement of holes through which the coolant is injected. The data output from the inputter/outputter 10 includes a result of the cooling simulation. The inputter/outputter 10 may be connected to an external device such as a keyboard, a mouse, a display, or an external storage device.

The calculator 20 is provided with, for example, a central processing unit (CPU). The calculator 20 reads and executes a cooling simulation program stored in the storage 30. Specifically, the calculator 20 calculates a flow velocity of the coolant on a surface of the workpiece by performing a thermal fluid simulation, calculates a heat transfer coefficient or reads and acquires the heat transfer coefficient from the storage 30 based on the temperature of the surface of the workpiece and the calculated flow velocity of the coolant, and calculates the temperature change of the surface of the workpiece using the acquired heat transfer coefficient.

The storage 30 is provided with a storage mechanism such as a solid state drive (SSD) or a hard disk drive (HDD). A cooling simulation program is stored in the storage 30. The cooling simulation program includes a thermal fluid simulation program. The storage 30 may store a magnetic field analysis program, a thermal analysis program, a structure analysis program, a stress/strain analysis program, and a circuit analysis program.

The storage 30 also stores a relation (hereinafter, also referred to as a “Tvh relation”) between a temperature Ts (hereinafter, also referred to as the “workpiece surface temperature Ts”) of the surface of the workpiece, a flow velocity v of the coolant, and a heat transfer coefficient h. The storage 30 may store the Tvh relation as a table, may store the Tvh relation as a mathematical expression, or may store the Tvh relation in another format. Note that the “heat transfer coefficient” is a heat transfer amount per unit area, unit temperature, and unit time at an interface between two types of objects.

As illustrated in FIG. 1B, the calculator 20 includes a controller 21, a magnetic field analyzer 22, a calorific value calculator 23, a heat treatment analyzer 24, a physical property value updater 25, a circuit analyzer 26, and a thermal fluid analyzer 27. The controller 21, the magnetic field analyzer 22, the calorific value calculator 23, the heat treatment analyzer 24, the physical property value updater 25, the circuit analyzer 26, and the thermal fluid analyzer 27 (hereinafter, collectively referred to as the “respective units 21 to 27”) may be configured by independent hardware resources, or may be virtually configured by executing a program.

The controller 21 controls the respective units 22 to 27, exchanges commands and data between the respective units 22 to 27, and exchanges data between the inputter/outputter 10 and the storage 30. The controller 21 also controls the number of iterations and step time of coupled analysis or monitors a temperature of a designated part. Note that the “coupled analysis” means performing analysis while considering complex mutual influences of a plurality of physical phenomena.

The magnetic field analyzer 22 performs magnetic field analysis by a finite element method based on a Maxwell's electromagnetic equation. Specifically, the magnetic field analyzer 22 calculates a magnetic flux distribution generated around a heating coil and an eddy current generated in the vicinity of the surface of the workpiece with a temporal change in the distribution by using an A method or an A-φ method capable of performing frequency response analysis among finite element methods.

The magnetic field analyzer 22 divides the workpiece, the heating coil, and a peripheral space into a plurality of elements. Therefore, the data input to the magnetic field analyzer 22 is, for example, as follows.

First, as a FEM model for magnetic field analysis in which the workpiece, the heating coil, and the peripheral space are divided into a plurality of elements at each node, there are combinations (hereinafter, simply referred to as “element information”) of node information indicated by the coordinates and node information constituting each element.

Second, as material physical property information regarding each material of the workpiece and the heating coil, there are electric conductivity and relative permeability for each metal structure, and both have temperature dependency.

Third, as information regarding analysis conditions, there are a frequency of a high-frequency induction heating power supply and a heating coil current or a heating coil voltage.

Fourth, there is temperature information at each node in the FEM model for magnetic field analysis. Note that a room temperature is input to the initial value of the temperature information and is sequentially rewritten by the controller 21.

The magnetic field analyzer 22 sets an inflow and outflow surface of a current or a voltage in a cross section of the heating coil using the FEM model for magnetic field analysis, obtains a magnetic flux distribution based on the setting, obtains an eddy current distribution based on the magnetic flux distribution, and calculates a Joule loss amount (heat generation density amount). That is, the magnetic field analyzer 22 calculates the Joule loss amount for each element in the FEM model for magnetic field analysis. In addition, the magnetic field analyzer 22 outputs data indicating the Joule loss amount for each element to the calorific value calculator 23.

The calorific value calculator 23 calculates a calorific value of each element from the Joule loss amount of each element input from the magnetic field analyzer 22 and outputs the calorific value to the heat treatment analyzer 24.

The information input to the calorific value calculator 23 is node information and element information defined by the coordinates set in the workpiece, and both the node information and the element information are defined for each FEM model for magnetic field analysis and each FEM model for heat treatment analysis. The calorific value calculator 23 performs mapping processing on the node information and the element information in the FEM model for magnetic field analysis and the node information and the element information in the FEM model for heat treatment analysis. The calorific value calculator 23 obtains a calorific value of each element in the FEM model for heat treatment analysis, and outputs the calorific value to the heat treatment analyzer 24 directly or via the controller 21.

As illustrated in FIG. 2A, in the workpiece, the temperature, the structure, and the stress/strain of each portion are correlated with each other. Therefore, the heat treatment analyzer 24 predicts the temperature and strain of each node, the stress for each element, the metal structure, and the like set in the FEM model for heat treatment analysis by performing coupled analysis on the mutual relation. For example, phase transformation occurs when the temperature changes in any portion of the workpiece. Conversely, when the phase transformation occurs, latent heat is generated and absorbed. When the phase transformation occurs non-uniformly in the workpiece, the volume locally changes and the stress is generated. Conversely, when the stress is generated, this affects the occurrence of the phase transformation. When the workpiece is deformed, a deformed portion generates heat or absorbs heat. When a temperature difference occurs inside the workpiece, the stress is generated. When the stress is generated, the strain is generated.

The heat treatment analyzer 24 divides the workpiece into a plurality of elements to analyze the above correlation using the finite element method, and performs analysis for each element while correlating the temperature, the elastoplastic structure, and the phase transformation. The heat treatment analyzer 24 performs analysis using a heat conduction equation or the like based on the calorific value for each element input from the calorific value calculator 23, and calculates the temperature and the deformation amount of each node, the stress/strain of each element, and the metal structure (metal structure volume fraction) in the FEM model for heat treatment analysis. Note that the metal structure volume fraction represents a ratio of a structure of steel, for example, ferrite, pearlite, austenite, martensite, or bainite. The stress/strain may be data-converted not for each element but for each node.

The data input to the heat treatment analyzer 24 is, for example, as follows.

First, as an FEM model for heat treatment analysis regarding the shape and dimensions of the workpiece, there are node information indicated by the coordinates and a combination of nodes (element information) constituting each element.

Second, as physical property information of steel constituting the workpiece, there are phase transformation characteristic information such as an isothermal transformation diagram (TTT: Time-Temperature-Transformation diagram), a continuous cooling transformation curve (CCT: Continuous-Cooling-Transformation diagram), austenite transformation temperature information (TTA: Time-Temperature-Austenitization diagram), and a martensite transformation temperature, thermal conduction characteristic information regarding thermal conductivity, specific heat, density, and latent heat, and stress/strain physical property information such as a Young's modulus, a Poisson's ratio, a linear expansion coefficient, a yield point, a work-hardening coefficient, a transformation expansion coefficient, and a transformation plastic coefficient.

Third, as information for assuming a cooling step of the workpiece, a value of the heat transfer coefficient h is defined as a thermal boundary condition on a cooling surface of the workpiece. The heat transfer coefficient h will be described later.

Fourth, there is information regarding the calorific value at each node defined in the FEM model for heat treatment analysis. This is input from the calorific value calculator 23.

Fifth, as information as the analysis condition, there are a heating time, a cooling time, the number of times of coupling, and the like.

The heat treatment analyzer 24 outputs data indicating the temperature of each node and the metal structure volume fraction of each element in the FEM model for heat treatment analysis to the physical property value updater 25 directly or via the controller 21, and outputs data indicating deformation of the workpiece to the thermal fluid analyzer 27 directly or via the controller 21.

The physical property value updater 25 receives the data indicating the temperature of each node and the metal structure volume fraction of each element in the FEM model for heat treatment analysis from the heat treatment analyzer 24, calculates the temperature of each node and the electric conductivity and relative permeability of each element in the FEM model for magnetic field analysis based on the data, and outputs the calculated data to the magnetic field analyzer 22 directly or via the controller 21. The temperature of each node and the electric conductivity and relative permeability of each element affect a penetration depth.

For example, as a circuit simulation, the circuit analyzer 26 performs calculation using a circuit equation for an electrical circuit of a high-frequency induction heating power supply, a matching device, a high-frequency transformer, and a heating coil to obtain a coil current or a coil voltage, and outputs the result to the magnetic field analyzer 22. As a result, it is also possible to evaluate a temporal variation of the induction heating phenomenon between the heating coil and the workpiece.

In a high-frequency quenching device, an LCR resonance circuit is used to apply power at a frequency under a constant condition to a heating coil to perform high-frequency induction heating on the workpiece. However, due to a change in a temperature distribution of the workpiece, the circuit load constantly varies, and the coil current, the coil voltage, and the resonance frequency also vary. As a method for controlling the high-frequency power supply, there is a method for controlling any one of the coil current, the coil voltage, and the input power constantly. In the present embodiment, the analysis result of the magnetic field analyzer 22 is used as input data of the circuit analyzer 26, and the analysis result of the circuit analyzer 26 is used as input data of the magnetic field analyzer 22, so that the magnetic field analysis and the circuit analysis can be linked, and high accuracy of a high-frequency quenching simulation can be achieved.

As illustrated in FIG. 2B, the thermal fluid analyzer 27 performs a thermal fluid simulation using computational fluid dynamics based on a structure model representing a configuration of a cooling device. The structure model includes information such as a shape of the cooling jacket, a shape of the workpiece, a positional relation between an injection port of the coolant in the cooling jacket and the workpiece, and a direction in which the coolant is injected from the cooling jacket.

Data indicating the physical property and the flow rate of the coolant is input to the thermal fluid analyzer 27 via the inputter/outputter 10. In addition, temperature data including a workpiece surface temperature and data indicating a deformation amount of the workpiece are input from the heat treatment analyzer 24. Based on the input data, the thermal fluid analyzer 27 performs flow analysis of the coolant by a thermal fluid simulation, and calculates the flow velocity of the coolant on the surface of the workpiece. Note that the thermal fluid analyzer 27 may calculate the temperature and pressure of the coolant in addition to the flow velocity of the coolant on the surface of the workpiece.

The controller 21 receives the flow velocity of the coolant on the surface of the workpiece from the thermal fluid analyzer 27, acquires the heat transfer coefficient h with reference to the relation (Tvh relation) between the workpiece surface temperature Ts, the flow velocity v of the coolant, and the heat transfer coefficient h stored in the storage 30, and outputs the heat transfer coefficient h to the heat treatment analyzer 24.

FIG. 3 is a graph illustrating a relation (Tvh relation) between the workpiece surface temperature Ts, the flow velocity v of the coolant, and the heat transfer coefficient h, in which a horizontal axis represents the workpiece surface temperature Ts and a vertical axis represents the heat transfer coefficient h on the workpiece surface.

FIG. 3 illustrates an example of a case where water is used as the coolant. The Tvh relation is not limited to that illustrated in FIG. 3 . The Tvh relation illustrated in FIG. 3 may be obtained by experiment, simulation, or model calculation. The heat transfer coefficient h at each workpiece surface temperature Ts and each flow velocity v is determined in consideration of the boiling phenomenon of the coolant.

Next, an operation of the cooling simulation device 1 according to the present embodiment, that is, a cooling simulation method according to the present embodiment will be described.

In the quenching treatment of the workpiece, a heating step and a cooling step are continuously performed. As described above, in the heating step, the workpiece is heated to a temperature equal to or higher than the austenite transformation point by, for example, high-frequency induction heating, and in the cooling step, the workpiece is rapidly cooled by, for example, injecting the coolant.

By the heating simulation, an initial state of the cooling simulation can be determined. For example, the initial value of the temperature of the surface of the workpiece and the initial value of the temperature inside the workpiece can be determined by the heating simulation. Note that the cooling simulation may be performed without performing the heating simulation. In this case, the initial value of the temperature of the surface of the workpiece and the initial value of the temperature inside the workpiece in the cooling simulation are input from the outside.

First, the simulation of the heating step will be described.

FIG. 4 is a flowchart illustrating a heating simulation method in the present embodiment.

As illustrated in FIG. 2A and step S91 of FIG. 4 , various data are input to the calculator 20 via the inputter/outputter 10. The input data may be stored in the storage 30.

Next, as illustrated in step S92, the magnetic field analyzer 22 performs magnetic field analysis, and outputs data indicating the Joule loss amount for each element to the calorific value calculator 23. At this time, the circuit analyzer 26 performs the circuit simulation and cooperates with the magnetic field analyzer 22.

Next, as illustrated in step S93, the calorific value calculator 23 calculates a calorific value in each element and outputs the calorific value to the heat treatment analyzer 24.

Next, as illustrated in step S94, the heat treatment analyzer 24 performs coupled analysis, calculates the temperature of each node and the metal structure volume fraction of each element, and outputs the temperature and the metal structure volume fraction to the physical property value updater 25.

Next, as illustrated in step S95, the physical property value updater 25 calculates the temperature of each node and the electric conductivity and relative permeability of each element, and updates the physical property data. Then, the updated physical property data is output to the magnetic field analyzer 22.

Next, as illustrated in step S96, when the number of times of coupling does not reach the designated number, the process returns to step S92. When the number of times of coupling reaches the designated number, the heating simulation ends.

As described above, by performing the heating simulation, a state of the workpiece at a final time point of the heating step, that is, a temperature distribution, a metal structure volume fraction distribution, and a stress/strain distribution can be estimated. The state of the workpiece can be set as an initial state of a cooling simulation described below.

Next, the simulation of the cooling step will be described.

First, a cooling method assumed in the present embodiment will be described.

FIG. 5 is a plan view illustrating a cooling device assumed in the present embodiment.

FIG. 6 is an end view illustrating the cooling device assumed in the present embodiment.

As illustrated in FIGS. 5 and 6 , a housing 110 is provided in a cooling device 101 assumed in the present embodiment. A liquid supply pipe 120 is connected to the housing 110. Although the number of liquid supply pipes 120 is arbitrary, FIGS. 5 and 6 illustrate an example in which the number is four. A cooling jacket 130 is provided in the housing 110. A shape of the cooling jacket 130 is, for example, a tubular shape extending in a vertical direction. The cooling jacket 130 is provided with a large number of holes 131. The holes 131 may be arranged regularly or irregularly.

When the quenching treatment is performed on a workpiece 100, the workpiece 100 is heated to a temperature equal to or higher than the austenite transformation point by a method such as high-frequency induction heating as described above. Next, the workpiece 100 is disposed in the cooling jacket 130 and rotated. In this state, a coolant 200 is supplied into the housing 110 through the liquid supply pipe 120. The coolant 200 is, for example, water. The coolant 200 passes through the hole 131 of the cooling jacket 130 while expanding in a space 140 between the housing 110 and the cooling jacket 130, and is injected to the workpiece 100. When the coolant 200 comes into contact with the workpiece 100, the coolant 200 takes the heat from the workpiece 100 to cool the workpiece 100.

Next, a cooling simulation method will be described.

In the present embodiment, a step in which the coolant 200 described above comes into contact with the workpiece 100 to cool the workpiece 100 is simulated, and a temperature change of each portion of the workpiece 100 is calculated.

FIG. 7 is a flowchart illustrating the cooling simulation method according to the present embodiment.

Note that FIG. 7 mainly illustrates the cooperative operation of the thermal fluid analyzer 27 and the heat treatment analyzer 24, and omits other operations.

Cooling simulation conditions, for example, an initial state of the workpiece, a shape of the cooling jacket, and information of the coolant are previously input to the inputter/outputter 10 of the device 1. The initial state of the workpiece includes, for example, an initial value of a temperature distribution inside the workpiece, an initial value of a temperature distribution of a surface of the workpiece, an initial value of a metal structure volume fraction distribution, and an initial value of a stress/strain distribution. The initial state of the workpiece may be determined by the heating simulation described above, or may be input from the outside. The information on the coolant includes a physical property, a temperature, and a flow rate of the coolant. The cooling simulation conditions are stored in the storage 30. The calculator 20 reads the cooling simulation program stored in the storage 30 and executes the cooling simulation program. In this way, the device 1 performs the cooling simulation.

First, as illustrated in step Si of FIG. 7 , the calculator 20 reads an initial value of the workpiece surface temperature Ts from the storage 30. In this simulation, a large number of minute portions are set for at least a part of the workpiece 100, for example, a quenching target portion, and an initial value of the workpiece surface temperature Ts is read for each minute portion. A part of the minute portion constitutes a surface of the workpiece 100.

Next, as illustrated in step S2 of FIGS. 2B and 7 , the thermal fluid analyzer 27 of the calculator 20 performs a thermal fluid simulation. The thermal fluid simulation can be performed by various methods. In the present embodiment, for example, a thermal fluid simulation using computational fluid dynamics is performed. As a result, a flow of the coolant 200 in the cooling device 101 is analyzed. As a result, the flow velocity v of the coolant 200 on the surface of the workpiece 100 is calculated.

In this simulation, the surface of the workpiece 100 is divided into a large number of minute regions, and the flow velocity v of the coolant 200 is calculated for each minute region. That is, a distribution of the flow velocity v of the coolant 200 on the surface of the workpiece 100 is calculated. The flow velocity v is, for example, the velocity of the coolant 200 in a direction parallel to the surface of the workpiece 100. Note that the minute portion of the workpiece 100 and the minute region of the surface may correspond to each other on a one-to-one basis, but may not necessarily correspond to each other on a one-to-one basis. In addition to the flow velocity v of the coolant 200 on the surface of the workpiece 100, the distribution of the temperature Tq of the coolant 200 and the pressure P of the coolant 200 on the surface of the workpiece 100 may be calculated by the thermal fluid simulation.

Next, as illustrated in step S3, the calculator 20 refers to the Tvh relation stored in the storage 30 to acquire the heat transfer coefficient h based on the initial value of the workpiece surface temperature Ts and the flow velocity v. For example, when the Tvh relation is stored in the storage 30 as a table, the calculator 20 specifies a cell corresponding to the initial value of the workpiece surface temperature Ts and the flow velocity v in the table, and reads a value stored in the cell. When the Tvh relation is stored in the storage 30 as a mathematical expression, the calculator 20 substitutes the initial value of the workpiece surface temperature Ts and the flow velocity v into the mathematical expression to calculate the heat transfer coefficient h. The heat transfer coefficient h is also acquired for each minute region. That is, the calculator 20 acquires the distribution of the heat transfer coefficient h on the surface of the workpiece 100.

Next, as illustrated in step S4, the heat treatment analyzer 24 of the calculator 20 calculates the temperature change of the workpiece 100 based on the heat transfer coefficient h. This calculation is performed by, for example, as described above, coupled analysis of thermal analysis, structure analysis, and stress/strain analysis. As a result, the temperature change of the entire workpiece 100 is calculated, and as a part thereof, the change amount ATs of the workpiece surface temperature Ts is also calculated. However, the temperature change may be calculated by a method other than the above-described coupled analysis.

Next, as illustrated in step S5, the workpiece surface temperature Ts after the temperature change is calculated. That is, (Ts+ΔTs) is set as a new workpiece surface temperature Ts.

Next, the process returns from step S6 to step S1, and the new workpiece surface temperature Ts is read. As described above, the cooling simulation is continued by repeating steps S1 to S6. Then, when the number of times of coupling reaches the designated number, the cooling simulation ends.

In this way, the change in the temperature distribution inside the workpiece 100 in the cooling step is calculated, and the metal structure (metal structure volume fraction) distribution, the residual stress distribution, the hardness distribution, and the deformation amount of the workpiece 100 after the cooling step are calculated. As a result, it can be determined whether or not the characteristics of the workpiece 100 after the quenching treatment satisfy a required level.

Next, effects of the present embodiment will be described.

In the present embodiment, it is not necessary to model and calculate the boiling phenomenon by previously acquiring the relation (Tvh relation) between the workpiece surface temperature Ts, the flow velocity v of the coolant, and the heat transfer coefficient h and performing the cooling simulation using the relation. That is, by previously acquiring the Tvh relation, when the workpiece surface temperature Ts and the flow velocity v are given, the heat transfer coefficient h of the workpiece surface can be immediately acquired. As a result, a simulation with high accuracy can be performed in a short calculation time.

As illustrated in FIG. 3 , when the flow velocity of the coolant is higher, the heat transfer coefficient is higher. In addition, at each flow velocity, the heat transfer coefficient takes a maximum value when the workpiece surface temperature is around 100° C., and the heat transfer coefficient decreases regardless of whether the temperature is higher or lower than the temperature around 100° C. This is considered to be that because water as the coolant does not boil in a temperature range where the workpiece surface temperature is significantly lower than 100° C., the heat transfer coefficient increases as the temperature increases.

On the other hand, when the workpiece surface temperature is around 100° C., the coolant starts to boil. As the workpiece surface temperature increases, a mode of boiling changes from nucleate boiling to film boiling via transition boiling. Therefore, it is considered that the higher the workpiece surface temperature, the more the contact between the workpiece and the coolant is hindered by the steam, and the heat transfer coefficient decreases. As described above, although the mechanism of the boiling phenomenon is complicated, according to the present embodiment, since the heat transfer coefficient is a value incorporating the boiling phenomenon, it is not necessary to simulate the boiling phenomenon in the cooling simulation, and the calculation time can be shortened.

According to the present embodiment, in the process illustrated in step S2 of FIG. 7 , the surface of the workpiece 100 is divided into a large number of minute regions, and the workpiece surface temperature Ts and the flow velocity v of the coolant are calculated for each minute region. As a result, in the process illustrated in step S3, the heat transfer coefficient h can be acquired for each minute region. As a result, as compared with a case where a single value is used as the heat transfer coefficient, the temperature inside the workpiece 100 can be calculated with high accuracy, and the accuracy of the cooling simulation can be remarkably improved.

Further, according to the present embodiment, as illustrated in FIG. 2B, the thermal treatment analysis of the workpiece 100 is performed in conjunction with the thermal fluid analysis of the coolant 200. Data is fed back to each other between the thermal fluid analysis and the heat treatment analysis. In addition, the heat treatment analysis is a coupled analysis of thermal analysis, structure analysis, and stress/strain analysis. As a result, it is possible to predict the hardness, the deformation amount, and the residual stress of the workpiece after the quenching treatment. By feeding back the deformation of the workpiece 100 in the cooling step to the thermal fluid analysis, it is possible to consider an influence of the deformation of the workpiece 100 on the circulation of the coolant 200. As a result, the accuracy of the cooling simulation is further improved.

Furthermore, according to the present embodiment, the initial value of the cooling simulation can be determined by the heating simulation. As a result, the accuracy of the cooling simulation is further improved.

Second Embodiment

FIG. 8 is a flowchart illustrating a cooling simulation method according to the present embodiment.

As illustrated in FIG. 8 , in the present embodiment, as illustrated in step S12, in addition to a flow velocity v of a coolant on a workpiece surface, a temperature Tq of the coolant and a pressure P of the coolant on the workpiece surface are also calculated by a thermal fluid simulation. Then, as illustrated in step S13, a heat transfer coefficient h is acquired based on the workpiece surface temperature Ts, the flow velocity v of the coolant, the temperature Tq of the coolant, and the pressure P of the coolant. A relation between the workpiece surface temperature Ts, the flow velocity v of the coolant, the temperature Tq of the coolant, the pressure P of the coolant, and the heat transfer coefficient h is stored in a storage 30.

This relation may be stored as, for example, a table or a mathematical expression. In a case of the mathematical expression, the heat transfer coefficient h is described as a function of the workpiece surface temperature Ts, the flow velocity v of the coolant, the temperature Tq of the coolant, and the pressure P of the coolant as follows.

h=f(Ts, v, Tq, P)

In order to calculate the heat transfer coefficient h more accurately, a parameter may be added to the above-described function.

Steps other than the above steps in the present embodiment are similar to those in the first embodiment.

According to the present embodiment, by acquiring the heat transfer coefficient h in consideration of the temperature Tq and the pressure P of a coolant 200 on the surface of the workpiece 100 in addition to the workpiece surface temperature Ts and the flow velocity v of the coolant, a more accurate simulation can be performed. Configurations, operations, and effects other than those described above in the present embodiment are similar to those in the first embodiment.

Third Embodiment

Next, a method of cooling a workpiece using the cooling simulation method, the cooling simulation program, or the cooling simulation device described above will be described.

FIG. 9 is a flowchart illustrating a method of cooling a workpiece according to the present embodiment.

First, as illustrated in step S21 in FIG. 9 , a plurality of cooling jackets having different shapes is assumed, and data indicating the shapes of the cooling jackets is created. The assumed cooling jackets may have a shape such as the shape of the cooling jacket 130 illustrated in FIGS. 5 and 6 . The data indicating the shapes of the cooling jackets may include, for example, a diameter and an axial length of each cooling jacket, and the size, number and arrangement of holes through which the coolant is injected.

Next, as illustrated in step S22 in FIG. 9 , cooling simulation is performed using the data created in step S21 to calculate the temperature change inside the workpiece. This cooling simulation method is as described in the first or second embodiment described above. The cooling simulation may be performed using the cooling simulation device described in the first embodiment, or may be performed by causing a general-purpose computer to execute the cooling simulation program.

The cooling simulation program is a cooling simulation program for predicting the temperature change inside the workpiece when a coolant is brought into contact with the surface of the workpiece. This cooling simulation program causes a computer to calculate a flow velocity of the coolant on the surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculate the temperature change inside the workpiece based on the temperature of the surface of the workpiece and the calculated flow velocity.

Next, as illustrated in step S23 in FIG. 9 , the optimum shape of the cooling jacket is determined based on the result of the cooling simulation performed in step S22. For example, the characteristics of the workpiece after cooling is evaluated based on the calculation result of the metal structure (metal structure volume fraction) distribution, the residual stress distribution, the hardness distribution, and the deformation amount of the workpiece after cooling, and a cooling jacket that results in a workpiece having characteristics closest to the required characteristics is selected.

As illustrated in step S24 in FIG. 9 , a cooling jacket having the optimum shape determined in step S23 is actually manufactured.

Next, as illustrated in step S25 in FIG. 9 , a workpiece is cooled using the cooling jacket manufactured in step S24. The workpiece is heated to, for example, a temperature equal to or higher than the austenite transformation point before the cooling. As a result, quenching treatment can be performed on the workpiece.

According to the present embodiment, cooling conditions, for example, the shape of the cooling jacket can be optimized at a low cost in a short time. As a result, high accuracy and high quality of a workpiece after cooling, for example, a workpiece after quenching treatment can be achieved. For example, high accuracy of the shape of a workpiece after cooling is achieved so that the residual stress is controlled to reduce deformation, and then the surface state of a workpiece can be a desirable state.

Note that although in the present embodiment, an example in which a cooling condition to be optimized is the shape of the cooling jacket has been described, a cooling condition to be optimized is not limited to the shape of the cooling jacket and may be a physical property of the coolant, a flow rate of the coolant, a temperature of the coolant, a positional relation between the injection port of the coolant in the cooling jacket and the workpiece, a direction in which the coolant is injected from the cooling jacket, and the like.

Test Example

Next, a test example illustrating the effects of the first embodiment will be described.

FIG. 10A is a perspective transparent view illustrating a cooling device assumed and manufactured in the test example, and FIG. 10B is a diagram illustrating an initial value of the workpiece surface temperature Ts.

FIG. 11A is a diagram illustrating an appearance of a coolant calculated in the test example, and FIG. 11B is a diagram illustrating a flow velocity distribution.

As illustrated in FIG. 10A, a basic configuration of a cooling device 103 assumed in the present test example is similar to that of the cooling device 101 illustrated in FIGS. 5 and 6 . In the cooling device 103 assumed in the present test example, five liquid supply pipes 120 are connected to the housing 110. The cooling jacket 130 has a cylindrical shape, a height of 68 mm, and an inner diameter of 140 mm. The number of holes 131 is 330, and a diameter of each hole 131 is 2 mm.

A cylindrical rectifying plate 135 is provided between the cooling jacket 130 and the housing 110. The rectifying plate 135 is provided with 24 holes 136. Two holes 136 are arranged in a vertical direction and 12 holes are arranged in a circumferential direction. The shape of the workpiece 100 was a ring shape, the height thereof was 50 mm, the outer diameter thereof was 100 mm, and the inner diameter thereof was 80 mm. Water was used as the coolant 200. A flow rate of the coolant 200 was 200 L/min, and a temperature was 20° C.

Under the above conditions, the thermal fluid simulation was performed by the method described in the first embodiment. As illustrated in FIG. 11A, the coolant 200 overflows from the cooling device 103 and spreads over the entire side surface of the workpiece 100. As illustrated in FIG. 11B, the distribution of the flow velocity v of the coolant 200 is a distribution reflecting the distribution of the holes 131 of the cooling jacket 130.

In the present test example, the temperature change was calculated by performing the cooling simulation described in the first embodiment. In addition, the temperature change was measured by actually performing the cooling treatment. Hereinafter, a result of the simulation is referred to as a “calculated value”, and a measured value obtained by an actual cooling treatment is referred to as an “actual measured value”.

FIGS. 12A and 12B are graphs illustrating a workpiece surface temperature change with a horizontal axis representing a time and a vertical axis representing a temperature, in which FIG. 12A illustrates an actual measured value, and FIG. 12B illustrates a calculated value.

As illustrated in FIG. 10B, an initial temperature of a center portion 100 b of the workpiece 100 was set to 920° C., and initial temperatures of an upper portion 100 a and a lower portion 100 c were set to 870° C. The rotation speed of the workpiece 100 was set to 200 rpm.

As illustrated in FIG. 12A, in the actual measured value, the cooling rate was low for 0.5 seconds from the start of cooling, and increased after 0.5 seconds. After a lapse of 0.5 seconds, the temperature of the upper portion was lower than the temperature of the lower part at each time point. As illustrated in FIG. 12B, even in the calculated value, the cooling rate was low for 0.5 seconds from the start of cooling, and increased after 0.5 seconds. After a lapse of 0.5 seconds, the temperature of the upper portion was lower than the temperature of the lower part at each time point. As described above, according to the present test example, the cooling behavior was substantially matched between the actual measured value and the calculated value.

The embodiments described above are examples embodying the present invention, and the present invention is not limited to these embodiments. For example, in each of the above-described embodiments, addition, deletion, or modification of some components is also included in the present invention.

The present invention includes the following aspects.

Supplemental Note 1

A cooling simulation method for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece, the cooling simulation method including

calculating a flow velocity of the coolant on the surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculating the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.

Supplemental Note 2

The cooling simulation method according to supplemental note 1, in which a heat transfer coefficient on the surface of the workpiece is estimated based on the temperature of the surface of the workpiece and the flow velocity, and the temperature change inside the workpiece is calculated using the heat transfer coefficient.

Supplemental Note 3

The cooling simulation method according to supplemental note 2, in which a value of the heat transfer coefficient is determined in consideration of a boiling phenomenon of the coolant.

Supplemental Note 4

The cooling simulation method according to supplemental note 1, in which a temperature of the coolant on the surface of the workpiece and a pressure of the coolant are also calculated by the thermal fluid simulation, and the temperature change inside the workpiece is calculated based on the temperature of the surface of the workpiece, the flow velocity of the coolant, the temperature of the coolant, and the pressure of the coolant.

Supplemental Note 5

The cooling simulation method according to supplemental note 4, in which a heat transfer coefficient on the surface of the workpiece is estimated based on the temperature of the surface of the workpiece, the flow velocity of the coolant, the temperature of the coolant, and the pressure of the coolant, and the temperature change inside the workpiece is calculated using the heat transfer coefficient.

Supplemental Note 6

The cooling simulation method according to any one of supplemental notes 1 to 5, in which when the temperature change inside the workpiece is calculated, a structure, a stress, and a strain of the workpiece are also calculated.

Supplemental Note 7

The cooling simulation method according to supplemental note 6, in which a deformation of the workpiece is fed back to the thermal fluid simulation.

Supplemental note 8

The cooling simulation method according to any one of supplemental notes 1 to 7, in which the temperature change inside the workpiece is fed back to the thermal fluid simulation.

Supplemental Note 9

The cooling simulation method according to any one of supplemental notes 1 to 8, in which an initial value of the temperature of the surface of the workpiece and an initial value of the temperature inside the workpiece are obtained by a simulation when high-frequency induction heating is performed on the workpiece.

Supplemental Note 10

A cooling simulation program for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece, the cooling simulation program causing a computer to

calculate a flow velocity of the coolant on a surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculate the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.

Supplemental Note 11

A cooling simulation device for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece, the cooling simulation device including:

a calculator that calculates a flow velocity of the coolant on the surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculates the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.

Supplemental Note 12

The cooling simulation device according to supplemental note 11, further including:

a storage that stores a relation between the temperature of the surface of the workpiece, the flow velocity of the coolant, and the heat transfer coefficient on the surface, in which

the calculator acquires the heat transfer coefficient from the storage based on the temperature of the surface of the workpiece and the calculated flow velocity, and calculates the temperature change inside the workpiece using the read heat transfer coefficient.

Supplemental Note 13

A method of cooling a workpiece, including:

determining a cooling condition by the cooling simulation method according to any one of supplemental notes 1 to 9; and

cooling the workpiece under the determined condition.

Supplemental Note 14

The method of cooling a workpiece according to supplemental note 13, in which

the cooling condition includes a shape of a cooling jacket, and

in the cooling the workpiece, a cooling jacket having the shape determined in the determining the cooling condition is used. 

What is claimed is:
 1. A cooling simulation method for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece, the cooling simulation method comprising calculating a flow velocity of the coolant on the surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculating the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.
 2. The cooling simulation method according to claim 1, wherein a heat transfer coefficient on the surface of the workpiece is estimated based on the temperature of the surface of the workpiece and the flow velocity, and the temperature change inside the workpiece is calculated using the heat transfer coefficient.
 3. The cooling simulation method according to claim 2, wherein a value of the heat transfer coefficient is determined in consideration of a boiling phenomenon of the coolant.
 4. The cooling simulation method according to claim 1, wherein a temperature of the coolant on the surface of the workpiece and a pressure of the coolant are also calculated by the thermal fluid simulation, and the temperature change inside the workpiece is calculated based on the temperature of the surface of the workpiece, the flow velocity of the coolant, the temperature of the coolant, and the pressure of the coolant.
 5. The cooling simulation method according to claim 4, wherein a heat transfer coefficient on the surface of the workpiece is estimated based on the temperature of the surface of the workpiece, the flow velocity of the coolant, the temperature of the coolant, and the pressure of the coolant, and the temperature change inside the workpiece is calculated using the heat transfer coefficient.
 6. The cooling simulation method according to claim 1, wherein when the temperature change inside the workpiece is calculated, a structure, a stress, and a strain of the workpiece are also calculated.
 7. The cooling simulation method according to claim 6, wherein a deformation of the workpiece is fed back to the thermal fluid simulation.
 8. The cooling simulation method according to claim 1, wherein the temperature change inside the workpiece is fed back to the thermal fluid simulation.
 9. The cooling simulation method according to claim 1, wherein an initial value of the temperature of the surface of the workpiece and an initial value of the temperature inside the workpiece are obtained by a simulation when high-frequency induction heating is performed on the workpiece.
 10. A cooling simulation program for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece, the cooling simulation program causing a computer to calculate a flow velocity of the coolant on a surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculate the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.
 11. A cooling simulation device for predicting a temperature change inside a heated workpiece when a coolant is brought into contact with a surface of the workpiece, the cooling simulation device comprising: a calculator that calculates a flow velocity of the coolant on the surface of the workpiece by a flow analysis of the coolant by a thermal fluid simulation, and calculates the temperature change inside the workpiece based on a temperature of the surface of the workpiece and the calculated flow velocity.
 12. The cooling simulation device according to claim 11, further comprising: a storage that stores a relation between the temperature of the surface of the workpiece, the flow velocity of the coolant, and the heat transfer coefficient on the surface, wherein the calculator acquires the heat transfer coefficient from the storage based on the temperature of the surface of the workpiece and the calculated flow velocity, and calculates the temperature change inside the workpiece using the read heat transfer coefficient.
 13. A method of cooling a workpiece, comprising: determining a cooling condition by the cooling simulation method according to claim 1; and cooling the workpiece under the determined condition.
 14. The method of cooling a workpiece according to claim 13, wherein the cooling condition includes a shape of a cooling jacket, and in the cooling the workpiece, a cooling jacket having the shape determined in the determining the cooling condition is used. 